On 11/29/2010 02:04 AM, Michael S. Tsirkin wrote:
On Sun, Nov 28, 2010 at 05:13:41PM -0600, Anthony Liguori wrote:
On 11/28/2010 04:28 PM, Michael S. Tsirkin wrote:
But rather need to use ugly factory functions with all sorts of
DO_UPCAST. This is really unfriendly especially for writing test
cases.
Yes, I agree. Just moving memory allocation out of there
will fix most of the ugliness.
So here's a short list of things I've been working on that I don't
believe have nice implementations in C.
1) Factories with string based parameters with natural constructor
arguments.
This was the only item, right? So in fact, this is needed as part of
configuration file/command line/monitor parser.
I really see it more as an API interface. I think the best long term
architecture for QEMU is where qemu is launched as essentially a daemon
and is manipulated via an RPC interface to create an initial device
model, etc.
IMHO, this really should be separate from the device model.
The fact that qdev currently mixes the device model
with argument parsing is bad IMO. So we ended up with
saying
.driver = "PCI"
in hw/pc_piix.c instead of an instance of the structure.
There's no compile-time check that the correct string
is used and that is pretty bad IMO.
Indeed.
Yes, this makes it easier to add new properties, but making it easy is
exactly the wrong thing to do because we really have to support such
properties forever.
One advantage of having a factory and the objects in a single place is
that the factory is the long term supported interface and the objects
can evolve in a more natural fashion.
So how about a compromise: libqemu written in C, with APIs that should
not deal with string parsing at all, and should above all else make
sense:
i8254_init_drift_mode
i8254_init_catchup
net_set_link_up
net_set_link_down
(and it really needs to be C for portability: so that management
written in C can use it).
This API should be properly versioned, with a backwards compatibility
story, and we should be careful about adding interfaces there.
On top of this you can have a management interface written in
any other language, and have that deal with string parsing.
I still dislike the idea of implementing an object system in C. Besides
reinventing vtables, we'll have to also reinvent RTTI to allow for safe
upcasting (which is unavoidable).
But really, let's defer this discussion for when patches are available.
I understand your objections but I'm pretty convinced that the code will
speak for itself when it's ready.
Regards,
Anthony Liguori
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